Geol Paläeont Mitt Ibk Vol 013-0239-0275

Ceol.Paläont.Mitt Innsbruck ISSN 0378-6870 Bd.13 11 S.239-275 I b k , Jänner 1986 THE FIRST EVIDENCE OF THE UNUMA ECHINATUS RADIOLARIAN ZONE IN THE RUDABÁNYA MTS (NORTHERN HUNGARY) by J GRILL & H KOZUR 1) Zusammenfassung Die Unuma echinatus Radiolarien-Zone wurde nun auch im Rudabanya-Gebirge nachgewiesen Diese Zone war längere Zeit nur aus Tiefwasserablagerungen in der Umrandung des Pazifik bekannt (die Index-Art war sogar nur in Japan gefunden worden) Später wurde die Unuma echinatus-Zone in Tiefwasserablagerungen des Aalenian bis Mittelbajocian des Bükk-Gebirges nachgewiesen (KOZUR, 1984) Diese Ablagerungen wurden unterhalb des CCD sedimentiert Sie führen reichlich Unuma echinatus Im Rudabánya-Gebirge wurden die Sedimente mit vereinzelt Unuma echinatus ebenfalls in grưßeren Wassertiefen, jedoch nahe der CCD abgelagert Die Unuma echinatus-Zone konnte in zwei Subzonen untergliedert werden, die Lupherium officerense-Subzone (Aalenian bis básales Mittelbajocian) und die Yaocapsa mastoidea-Subzone (höheres Mittelbajocian) Im taxonomischen Teil werden mehrere neue Arten der Gattungen Foremanina, Canoptum, Pseudoeucyrtis, Hsuum und der neuen Gattung Pseudodictyomitrella beschrieben In einem Anhang (KOZUR & MOSTLER) werden neue Arten von Archaeodictyomitra beschrieben Summary The Unuma echinatus radiolarian zone could now also be found in the Rudabánya Mts For a longer time this zone was only known from deep water sediments of the Pacific margin (the index species was even unknown outside Japan) The Unuma echinatus zone (with rich occurrences of the index species) was later recognized also in deep water sediments of Aalenian to Middle Bajocian age of the Biikk Mts (KOZUR, 1984) deposited below the CCD In the Rudabánya Mts sediments with only few specimens of Unuma echinatus were deposited also in greater water depth, but near the CCD 1) authors' addresses: Dipl Geol József Grill and Dr sc Heinz Kozur, Hungarian Geological Institute, Népstadion út 14, H-1143 Budapest/ Hungary 239 Two subzones of the Unuma echinatus zone could be discriminated The lower Unuma echinatus zone (Lupherium officerense subzone) was correlated with the Aalenian to lowermost Middle Bajocian The upper Unuma echinatus zone (Yaocapsa mastoidea subzone was placed into the higher part of Middle Bajocian In the taxonomic part several new species of the genera Foremanina, Canoptum, Pseudoeucyrtis, Hsuum and of the new genus Pseudodictyomitrella n gen are described In an appendix by KOZUR & MOSTLER species of Archaeodictyomitra are described Introduction The Unuma echinatus radiolarian zone is typical for Aalenian to Middle Bajocian deep water sediments, often sedimented below the CCD Therefore for a long time this radiolarian fauna was only known from eugeosynclinal sequences in Japan with shales, manganese shales, black cherts, that are often connected with basic lavas KOZUR (1984) found this fauna also in the South Bükk Shalé Unit of Southern and Western Biikk Mts that consists of the Aalenian and Middle Bajocian of dark shales with some black or grey cherts, manganese nodules and in some places (e g Szarvaskó) huge amounts of pillow lavas The Unuma echinatus zone should be found in all sequences of the Tethyan Mobile Belt (KOZUR, in press, KOZUR & MOCK, in press) But this Middle Jurassic to Lower Cretaceous suboceanic to oceanic belt was later mostly subducted or metamorphosed (e.g Penninicum) The Unuma echinatus fauna can be expected also in those sedimentary areas primarily located between the Tethyan Mobile Belt and the shelf of Apulia or Europe These sequences were sedimentated partly below, partly above the CCD and have in general no basic volcanics The presence of the Unuma echinatus fauna could be therefore expected for the Jurassic sequence of the Rudabánya Mts Well preserved radiolarians of the Unuma echinatus zone could be found now in the Rudabánya Mts Some of these radiolarians are described here Stratigraphy Jurassic sediments cover about km2 in the studied area in the middle part of the Rudabánya Mts SW of Szalonna The location of the studied area is shown in figs and The Jurassic sequence overlies Upper Triassic pelagic limestones, often with tectonic contact It consists mainly of monotonous black to dark grey shales, marls, siliceous shales and manganeseshales, with some rhyolitic volcanics or subvolcanics, Middle-Upper Triassic limestone olistoliths and sometimes sandstone olistoliths This Jurassic sequence can be subdivided into threee members The Lower Member is about 300 m thick and conists of black, partly siliceous and manganese shales and marls The lower part of the Lower Member consists of black to dark grey marls with 9-55 % carbonate, 14-43 % quartz, 3-10 % chlorite, 4-20 % clay minerals, 2-14 % plagioklase Some interbedded dark limy marls to marly limestones as well as limestone olistoliths are present The marls are mostly unbedded, sometimes a lamination can be observed These beds were deposited in a basinal deep water facies, but above the CCD 240 Fig 1: Location of the Rudabanya Mts in northern Hungary (open square) The middle part of the Lower Member consists of black shales, siliceous shales, manganese shales, subordinately also lenses and thin beds of black or dark-grey cherts The shales consist of 30-60 % quartz, 38-63 % clay minerals + chlorite and 2-7 % plagioklase Pyrite (about %) is always present Some samples have a very low primary carbonate content Therefore the deposition of the sediments in the middle part of the Lower Member seems to be near to the CCD, a little above it for sediments with very low primary carbonate content and somewhat below the CCD for carbonate-free sediments All described radiolarians of the Unuma echinatus zone from the Rudabanya Mts derive from the middle part of the Lower Member This supports the above given facial data The Unuma echinatus zone is until now only known from deep water sediments of Japan and the Biikk Mts., deposited well below the CCD Interesting that this radiolarian fauna was found always in a sequence of black shales, mudstones, siliceous shales, manganese shales and dark cherts Siliceous limestones and cherty nodules of the same age from the Balaton Highland have never? yielded Unuma echinatus In the Rudabanya Mts this species is very rare inspite of an otherwise very rich radiolarian fauna In the Biikk Mts and in Japan Unuma echinatus is rather requent Therefore, Unuma echinatus seems to be restricted to sediments deposited below the CCD In sediments, deposited near or a little above the CCD, Unuma echinatus is already very rare.The upper part of the Lower Member consists of marls, limy marls and some beds of allodapical limestones Limestone olistoliths (maximum size m ) and slightly alterated rhyolitic clasts and some bodies of slightly alterated rhyolites are also present The marls are well laminated and the allodapical limestones are usually graded Slumping structures are locally present The mineral composition of the marls in the upper part of the Lower Member is similar to that of the marls in the lower part of the Lower Member The slightly alterated rhyolitic clasts indicate that rhyolites have already been eroded during the deposition of the upper part of the Lower Member The slightly alterated rhyolitic bodies always have tectoni- 241 Fig 2: Studied area in the middle part of the Rudabánya Mts The filled square indicates the sampling place of the sample GRILL 80 (Csehi-hegy) Circle: borehole Várboc-2 Dashed lines: Telekes side-valleys no and cal contact with the marls In spite of this tectonic contact we think that the rhyolitic bodies are probably contemporaneous or almost contemporaneous with the surrounding marls, because the soft marls and the big hard rhyolitic bodies surely reacted with different relative movements to the lateral pressure during the strong tectonization of the whole sequence Moreover, also the fact that the lower and middle parts of the Lower Member are quite free of rhyolitic bodies and rhyolitic clasts is a further indication for a nearly contemporaneous volcanism during the sedimentation of the upper part of the Lower Member The Middle Member is about 100 m thick and consists of dark grey marls with wavy bedding planes Numerous small sandstone olistoliths (max size m ) are present These sandstones are cross-bedded and consist of 40-70 % quartz, 1-10 % feldspar, 0-5 % mica and small pieces of rock fragments The intergrain matrix (10-30 %) consists of quartz, chlorite and sericite The marls contain 10-30 % carbonate Therefore this sequence is deposited above the CCD The Upper Member is about 300 m thick and consists of black laminated marls with big olistoliths of Triassic limestones and conglomeratic olistoliths with pebbles of limestones and rhyolites The marls consist of 10-20 % carbonate, 30-40 % quartz, % plagioclase, 10-25 % clay minerals and 20-30 % chlorite They contain also 242 less than 10 % quartz and mica clasts Rhyolitic tuffs are locally present (Bôdva valley) A Middle and Upper Triassic sequence can be reconstructed from the limestone olistoliths This Triassic development is quite different from the Triassic sequence that underlies the Jurassic beds (see figs 4, ) -=* i r Fig 3: Stratigraphie column of the investigated area - Hallstatt Limestone Formation - Zlambach Marl Formation - Lower Member of the Jurassic sequence - Middle Member of the Jurassic sequence - Upper Member of the Jurassic sequence I I The Jurassic sequence looks like a schistes lystré type (Caucasian subtype), but we don't know basic magmas yet, unlike the otherwise similar (but carbonate-free) South Biikk Shale Unit of the southern and western Biikk Mts and the Jurassic sequence of the Meliata Unit Above all in parts of the South Biikk Shale Unit thick pillow lavas are present (e.g near Szarvaskc? in the western Biikk Mts.) According to KOZUR (in press) and KOZUR & MOCK (in press) both the South Biikk Shale Unit and the Meliata Unit have in the Jurassic a Penninic development (as part of the Tethyan Mobile Belt) The Middle and Upper Members of the investigated Jurassic sequence show a very low grade metamorphosis (anchimetamorphic) and a slight cleavage oblique to the bedding plane can be observed The Lower Member is either quite unmetamorphic or its upper part shows the same very low grade metamorphosis like the Middle and Upper Members All investigated radiolarian faunas of the Rudabánya Mts (Csehihegy SW of Szalonna, borehole Várboc-2, Telekes side-valleys number and 8) belong to the Unuma echinatus zone According to the newest 243 ! ~r • r^s 1 i | d C o if 1 1 1 1 1 • 1 1 - / 1 - - -j 6-1 j e